Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$69.97	13.751%	$79.5916	$79.59	$79.60	$79.60
Purchase #2	$241.71	5.818%	$255.7727	$255.77	$255.75	$255.80
Purchase #3	$199.83	11.721%	$223.2521	$223.25	$223.25	$223.30
Purchase #4	$141.55	12.348%	$159.0286	$159.03	$159.05	$159.00
Purchase #5	$42.90	9.269%	$46.8764	$46.88	$46.90	$46.90
Purchase #6	$223.45	3.643%	$231.5903	$231.59	$231.60	$231.60
Purchase #7	$240.56	5.759%	$254.4139	$254.41	$254.40	$254.40
7 purchase totals =	$1,159.97		$1,250.5256	$1,250.52	$1,250.55	$1,250.60